Colchester Bantam 1600

I have just purchased a nice Colchester Bantam. Looking at several pictures of Bantams they show a third shaft running below the lead screw. On my Bantam there is a blanking plate where this shaft would be fitted. I have the original manual which came with the lathe, but the manual does not cove the operation of this shaft. What is it used for ?

I think it is a square bar with a on off reverse lever that slides along with the saddle.

Hi Peter

It's for a control shaft, there is an on off / forward reverse and brake lever usually on the right hand side of the apron, It's linked to a switch located at the rear of the headstock behind the splashguard, and also mechanically linked to the brake pad arrangement on the changegear side of the headstock. Maybe not all bantams were fitted with this arrangement, worth a good look at the Lathes.co.uk website.

Dave

Edited By JasonB on 10/02/2023 20:01:54

Oops I've answered the other post as well!

I've got a Bantam 2000; on this there are three shafts running along the front of the bed. The top one is the leadscrew, the middle one is a shaft with a keyway all along it, this operates the longitudinal and cross feeds. There is a third shaft of about 16 mm square section which is controlled by the forward/off/reverse lever located right hand side of the saddle.

How is the on/off function controlled on your Bantam? Any chance of a few pictures?

My Bantam is fitted with a Newton Tesla inverter package. Not had it running yet, just wiring up as we speak. All controls will be through the Newton Tesla control interface.

Sounds as if someone has removed the control shaft to save furtling in the innards to make the Newton Tesla package compatible with the original switched control scheme.

I re-wired the control switch so it became the input controls to the VSD. Maybe this boat has sailed?

I just came across this post. I am trying to do the exact same thing with my Mk1 1600. The previous owner fitted a single speed motor and VFD but the fwd/rev lever only turns the motor on in both positions with the old speed range switch used to reverse the motor.

I want to use the lever as it should be and the speed range switch to change betwwen50 and 100 hz. Problem is I only have 3 wires coming from the reversing switch, grey, orange and blue and I can't get anything but blue and orange connecting in both positions. How did you do yours?

#Michael Horley

According to the circuit diagram there is indeed a pole of the Kraus and Naimer cam switch the apron lever operates that is an open circuit when the lever is in the middle position, and closes when the lever is moved down or up for forward and reverse. In the original Colchester control circuit this energises the main contactor. There is another circuit which makes only when the lever is in the centre neutral position. This is wired into the emergency stop/no volt release circuit so it can only be reset when the apron lever is in the centre "off" position so the motor can't restart without a second confirming action.

There are also two poles which close circuits when the lever is moved to the "forward" position, and another two poles which close for the "reverse" position. These switch the motor connections directly, hence these four circuits are wired as a two pole changeover switch.

The High/Off/Low switch under the front of the machine is a different animal, but it also switched the motor connections directly.

I converted mine to VSD operation, so I used one pole forward to tell the VSD to run forward, and another pole to tell the VSD to run reverse, i.e. a single pole changeover switch. The other changeover pole is spare. The pole of the cam switch which was closed in the off position is wired into the E Stop circuit as per the original and gives a "only reset in Off" function as per the original scheme. This forces the user to select "Off" before pressing the reset button, and (with an associated control relay) gives an emergency stop function with a second action to achieve a reset, also a no volt release function. Note that this means the switch carries mixed voltages but these switches are designed for this duty and this is OK.

I used the original speed selection switch to tell the VSD to run at either 50Hz (= Low) or 100 Hz (= High). These were simple contact closures into the VSD digital inputs. Overall I tried to stick to the function of the original controls even if the wiring was different.

By the sound of your description you've only found the circuit which closes when the apron switch is in either run position. This is only part of the story, and either there are more wires to discover or the switch is faulty, or maybe the previous owner had OAWS (Over Active Wirecutter Syndrome) and ripped out some wires he didn't orter.

Unfortunately the wire colours mean nothing as they are not specified on the circuit schematic and I wouldn't have bothered to keep to them anyway. I did this stuff for a living and just followed my own star.

Understanding the Kraus and Naimer cam switch is a bit of a dark art, If someone has been ripping wiring out and not keeping a record of which terminal did what then you're struggling somewhat. However I notice Tony at lathes,co,uk in his notes on the Mk1 Bantam not only identifies the K&N switch part number but also an alternative. That might be worth pursuing. Alternatively Google Kraus and Naimer in your area and find a distributor, they should be able to give you a circuit diagram for the switch function of the particular part number of the switch you have to hand. Otherwise if you want me to diagnose the switch function for you I can (probably) do that (they're a bit of a beast to decode!) but you'll have to remove the switch and post it to me, I'm sure I've seen a function diagram for this switch in the K&N catalogue but I don't have a copy to hand.

Good luck and do keep us posted.

Rgds Simon

#Michael Horley

Re-reading my earlier post I need to warn you that the function of the Kraus and Naimer switch is achieved by wiring contacts in series and parallel, as well as having a cam internally that moves the individual contacts. They can be a bit of a mind bender to understand. But knowing that the original scheme had:

two contacts (i.e. four terminals) closed in forward, otherwise open

two contacts (again, this will be four terminals) closed in reverse, otherwise open

one circuit closed in off, otherwise open

one circuit closed in forward or reverse and open in off

gives you a fighting chance.

I'm imagining that the last two functions may be contacts wired in series or parallel to give the overall function.

HTH Simon

Edited By Simon Williams 3 on 19/08/2023 00:25:24

I removed the 3rd shaft from mine when I converted it to VFD control. It is so much easier to sweep out the swarf with it removed !

Many thanks Simon for your comprehensive answers. I think the PO has indeed removed all the other wires. It looks a bugger to remove the switch to check but I can't see any cut wires in the conduit. I have sussed the high/low side of it by programming the VFD to 50 and 100hz and that all works, just need to wire it into the switch when I get the fwd/rev sorted properly.

I have seen a video where someone has replaced the original F/R switch with a simple rotary switch operated by the original lever with a bit of fabrication. I may go down that route in the end.

TYhis is exactly what was done when my BL12-24 was converted, pre delivery, from a single phase motor to 3 phase and VFD.

Saves an awful lot of mbelt changing!

Control of speed and direction of rotation is all done by the control box. (Looks like a Newton Tesla to my unpracticed eye )

Howard